It's been traveling through space since 1977, but Voyager 1 still hasn't crossed the boundary that marks the end of our solar system.

Thirty-five years after it launched from the Earth, Voyager 1 can still communicate with scientists on Earth. And as we noted recently, the long-lived spacecraft is approaching the boundary of the solar system, though what it's finding there is surprising some researchers.

To scientists, the edge of our solar system is not the last planet (or dwarf planet), but rather a region called the heliopause. Basically, it marks the terminus of the heliosphere, or the area of space carved out by the solar wind. Where those particles streaming out from the sun meet the plasma of interstellar space, there you'll find the heliopause.

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As of April 2010, Ars Technica reports, Voyager 1 had reached a distance of 113 AU from the sun (1 AU is the earth-to-sun distance, or about 93 million miles). At this incredible distance, scientists figured the craft would be passing through the heliopause and departing our solar system. But not so, says a new study out today in Nature.

Way out where Voyage now travels, the solar wind has slowed to a light breeze, according to the craft's instruments. But what the research team led by Robert B. Decker did not see, however, is the solar wind being deflected in different directions. That's what you'd expect to find in the heliopause, where the plasma of the interstellar medium would smack into the solar wind. And the fact that it's not there means perhaps, after all this time, Voyager 1 still hasn't arrived at the solar system's border—though it has to be getting close. Decker says he expects Voyager 1 to cross the heliopause within the next year.